Mortar damage due to airborne sulfur compounds in a simulation chamber

The interaction between airborne sulfur compounds and mortars has been investigated. Simulation experiments were carried out in a flow chamber where temperature, relative humidity and SO2 concentration were controlled. Samples of lime, pozzolan and cement mortars were exposed for 90 days in air with 3 ppm of SO2 concentration, at 25°C temperature and 100% relative humidity. Following exposure, the mortar samples were studied by x-ray diffraction, infrared spectroscopy and high pressure liquid chromatography. The data obtained from bulk and surface analyses clearly show that the materials reacted with sulfur dioxide to form calcium sulfite hemi-hydrate and calcium sulfate dihydrate. The quantity of sulfite and sulfate measured depends on the physical and chemical properties of the three mortars, but is independent of their CaCO3 content. Formation of ettringite and thaumasite did not occur in the 90 day period taken into account in the present work.ResumeOn a étudié l'interaction entre les composés ambiants du soufre et le mortier. Des expériences de simulation ont été entreprises dans une chambre où la température, l'humidité relative et la concentration en SO2 étaient contrôlées. Des échantillons de mortier de chaux, de pouzzolane et de ciment ont été exposés pendant 90 jours à des concentrations de 3 ppm de SO2, à une température de 25°C et une humidité relative de 100%. Après leur exposition, les échantillons de mortiers ont été analysés par diffraction aux rayons-x, spectroscopie infrarouge et chromatographie liquide à haute pression. Les résultats des analyses à la surface et en masse montrent clairement que ces matériaux réagissent avec le dioxyde de soufre pour former des sulfites hémihydrates de calcium et des sulfates dihydrates de calcium. La quantité de sulfates et sulfites mesurés varie selon les propriétés physiques et chimiques des trois types de mortiers, mais elle est indépendante de leur contenu en CaCO3. Il ne s'est pas produit de formation d'ettringite et de thaumasite pendant les 90 jours pris en compte dans cette expérience.

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